changes in the genetic makeup of a population Flashcards
gene
a sequence of DNA nucleotides that codes for a particular trait.
allele
a variation of a gene.
genotype
a combination of alleles.
phenotype
observable traits that are caused by the genotype and environment.
traits can be monogenic or polygenic. what does that mean?
Traits can be monogenic- discontinuous (discrete) variation
Traits can be polygenic- continuous
gene pool?
all the alleles possessed by an entire population, which may potentially be passed on to the next generation.
allele frequency definition and equation
relative proportion of an allele in a population. Percentage or decimal
Allele frequency: 2(homozygotes) + (heterozygotes)/
2(total individuals) x 100
how do new alleles arise? how does allele frequency change?
New alleles arise with mutations
Allele frequency changes with changes to environmental pressures
define mutation
a change to DNA.
what cab mutations be?
neutral, beneficial, harmful
what is a mutagen?
neutral, beneficial, harmful
how are most mutations dealt with?
Most mutations are detected and repaired by enzymes
somatic mutations
in body cells. Only affects individual.
germline mutations
affect gametes. Passed to offspring.
what are the types of point mutation?
substitution and frameshift
what is a point mutation?
alters, adds or removes a nucleotide. Affect a single gene.
types of substitution mutations?
Silent
Missense
Nonsense
what is a silent mutation?
New codon that still codes for the same amino acid
what is a missense mutation?
The amino acid changes
The protein may be able to function depending on the amino acid changed
what is a nonsense mutation?
Creates a stop codon
No more amino acids can be coded for
what is a frameshift mutation?
one or two nucleotides are added or removed from the nucleotide sequence, altering every codon.
types of frameshift mutations?
Nucleotide insertion
Nucleotide deletion
what are block mutations? when does it occur? how is it caused? what are the affects?
affect large sections of a chromosome.
Usually occur during meiosis
Can be caused by mutagens
Serious or lethal
types of block mutations?
Duplication Deletion Inversion Insertion Translocation
what is duplication?
Multiple copies of the same gene
what is deletion?
Section removed
Often fatal
what is inversion?
Upside down
what is insertion?
Section of one chromosome breaks off and attached to another
what is translocation?
A whole chromosome or segment attaches to another chromosome or segment
what are the types of chromosomal abnormalities?
polyploidy
aneuploidy
what is chromosomal abnormality?
mutations involving whole chromosomes.
what is aneuploidy?what is it caused by?
presence of an abnormal number of a chromosome; an extra or one missing
Often caused by non-disjunction: two homologous chromosomes do not desperate in meiosis
what is polyploidy? who survives? what can it lead to?
more than two full sets of chromosome in every chromosome set.
Some animals and plants may survive
Humans do not survive
Can lead to speciation
how does variation occur?
Variation occurs due to different combinations of alleles- independent assortment, recombination, mutations, random mating
what are selection pressure?
conditions that influence allele frequency. Can be natural or artificial such as selective breeding.
what drives evolution?
Mutations and selection pressures drive evolution.
what is natural selection?
influence of environment pressures on allele frequency in a population that affect survival and reproduction. Individuals with advantageous phenotypes more likely survive.
what are environmental selection pressures?
Climate
Competition
Mates availability
predators
what are the environmental pressures influence on allele frequencies?
Variation- genetic differences in pop
Reproduction- alleles are heritable
Survival- not all survive to reproduce
Environmental selection pressures- some phenotypes are better suited
high adaptive value
High adaptive value phenotypes- survival of fittest
what is gene flow?
migration of individuals leading to a change in gene pool.
When not possible, populations are isolated
what is genetic drift? what ways can it occur?
Genetic drift: chance events that change the allele frequencies in a gene pool.
Small pop- death of an individual, loss of genetic diversity
Can occur when population decreases over time (bottleneck) or in a small founding pop (founder effect)
what is the bottleneck effect?
Individuals are drastically and quickly reduced by a random event eg. Natural disaster
Individuals survive by chance not phenotype
Allele frequency changes
Bottleneck effect is the impact on remaining- inbreeding leading to reduced variation and increased homozygous
Smaller pop = greater effect
Lower variation makes pop more vulnerable
what is the founder effect?
Small group from a population move to a new location and establish a new population.
Smaller gene pool
Increased inbreeding and lower variation
Environmental pressures usually differ which drive evolution
evolution?
change in genetic composition of a population over time.
what are the processes of evolution?
Natural selection drives Environmental selection pressures Genetic drift Mutations Populations evolve, not individuals
what is a species?
Species: a group of individuals that are genetically similar enough to produce fertile viable offspring when interbreeding. Gene pool is isolated from that of other species
how does genetic isolation occur?
Genetic isolation occurs due to prezygotic (before reproduction) or after reproduction (postzygotic)
what is prezygotic isolating mechanisms?
Prezygotic isolating mechanisms: prevent individuals from different populations interbreeding.
what are the types of prezygotic isolating mechanisms?
geographical, ecological, temporal, behavioural, structural or morphological, gamete mortality, sexual selection
geographical
Geographical (spatial)
Populations are separated by eg. A mountain
ecological
Ecological isolation (niche partitioning) Occupy same ecosystem but have different niches within that
temporal
Temporal isolation
Breeding cycles do not overlap
behavioural
Behavioural isolation
Mating calls and rituals are highly specific
Often result of sexual selection
structural morphological
Structural or morphological isolation
Reproductive organs are incompatible
gamete mortality
Gamete mortality
Egg and sperm fail to fuse in fertilisation
Signalling molecules may not be adequate
May not be able to support sperm of another species
Pollen may be blocked by a chemical barrier
define sexual selection. describe
Sexual selection: evolution has resulted in behaviour acting as a reproductive isolating mechanism.
Select a mate based on specific traits- good health, fitness, high adaptive value
Alleles of good traits are inherited
Animals may compete for mates
Conflicts ensure ‘fittest’ phenotypes win- creates a more favourable gene pool
define postzygotic isolating mechanisms
Postzygotic isolating mechanisms: prevent as zygote of two different species from developing into a fertile adult.
types of post zygotic isolating mechanisms?
hybrid inviability, reduced hybrid viability, hybrid sterility
hybrid inviability
Hybrid inviability: sperm from one species does successfully fertilise the egg from another species to from a hybrid but it has unmatched chromosomes- zygote does not survive.
reduced hybrid viability
Reduced hybrid viability: zygote survives but will not fully develop to reach adulthood.
hybrid sterility
Hybrid sterility: hybrids that reach adulthood usually are infertile.
Without homologous chromosomes, meiosis cannot occur to form gametes (at all or they are abnormal)
First generation of hybrids can be semi-fertile and can sometimes mate with another hybrid
Second generation is sterile and is an isolating mechanism (hybrid breakdown)
define speciation
the evolution of a species form an ancestral species.
define allopatric speciation
Allopatric speciation: population becomes divided by a geographical barrier.
Overtime different environmental selection pressures and or genetic drift drive changes
May eventually be unable to interbreed- different species
define artificial selection/selective breeding
humans decide which individuals may breed.
how does selective breeding occur? compared to GMO
Steps:
Determine desired trait
Interbreed those with trait
Select offspring with best form of trait and interbreed them
Continue until population reliably reproduced desired trait
Genetically modified organisms is a faster and more specific approach to this
how does selective breeding in plants work?
Higher quality food
Seeds collected from individuals with largest yield
Seeds are planted and cross pollinated with plants with similar traits
May be modified for disease resistance
selective breeding in animals?
Selected for physical quality, quality of produce
what are potential detrimental effects of selective breeding?
Decreases genetic variation of other alleles and increases homozygosity
Gene linkage means that selecting for one allele may result in the selection of other traits
Selective breeding reduces resistance to environmental change
Low genetic variation, all individuals similar
If environment changes, selective pressures change
Vulnerable
Selective breeding reduces biodiversity
Selectively bred replace wild varieties
Food security is at risk
Food arks and seed banks formed to reduce risk
Selective breeding can increase genetic abnormalities
Genetic diseases that are rare in wild are common in pure bred animals
Many recessive conditions but interbreeding has increased the frequency of alleles- increases chance of homozygous recessive conditions
